Nebraska City Southeast Interchange Increases Efficiency and Capacity
The $24.5 million Nebraska City Southeast interchange project, at the junction of U.S. Highway 75 and Nebraska Highway 2, is on track for an on-time completion, which will increase the road's efficiency and reduce the number and severity of collisions by eliminating an at-grade signalized intersection.
"The project is to resolve capacity issues," says Thomas W. Goodbarn, District 1 Engineer with the Nebraska Department of Transportation in Lincoln.
During the 1990s, the Nebraska Department of Roads (NDOR) created a bypass around Nebraska City, a municipality of about 7,350 people according to the U.S. Census. That project converted a two-lane road to a four-lane road. But the last interchange was not finished as money dried up, Goodbarn explains. The interchange continued as an at-grade intersection.
"It's a high-volume urban interchange," Goodbarn says. "The project gives Nebraska City a safe, efficient and attractive intersection of two of Nebraska's main highways."
The U.S. 75/Nebraska Highway 2 interchange is located on the south edge of Nebraska City, near a mall being redeveloped, other businesses and homes. Traffic volumes on Highway 2 exceed 10,000 daily, with 29 percent of the traffic heavy trucks. The intersection has had a higher than the state average of history of fatal collisions.
"It has been on the list to get finished for a long time," Goodbarn adds. "It will serve Nebraska well for safety and completing the four-lane complex around Nebraska City."
The 1-mile long compact interchange project was funded through the Build Nebraska Act. Money was dedicated to completing this and other projects.
Constructors Inc. of Lincoln, a division of Nebco, received the contract and began work in March 2016. Nebco is a 108-year-old corporation with 25 companies and 1,000 employees. It has been family-owned and operated for three generations. James P. Abel, the current Chairman and CEO, began his career with the company in high school, working at the firm's concrete pipe plant.
On this project, Constructors will provide grading; install culverts, mechanically stabilized earth walls and bridges; pave; seed and landscape; and install lighting. The company expects it will pave more than 85,000 cubic yards of concrete and 20,000 tons of asphalt.
Concrete Industries Nebraska City, another Nebco company, is supplying the concrete for the project and Constructors' 804 Plant in Lincoln the asphalt. More than 15 subcontractors are involved with the project, including Pink Grading of Omaha and United Contractors of Johnston, Iowa.
The new configuration includes two, two-lane, 174-foot-long bridges, with NU-2000, concrete girders and jump spans on the side. Mechanically stabilized earth walls bring Highway 2 up and over 75. Near the mall, the MSE walls are 860 feet long and 38 feet tall at its highest location. In other sections on the Nebraska Highway 2 section, the MSE walls are about 25 to 30 feet tall, raising the grade. It will have a single-point interchange below.
"Basically, what we have done is elevate Highway 2 over 75, with two new overpasses," says Mike Habegger, Project Manager for NDOR. "We had pretty substantial vertical fills."
Once complete, the new interchange will not allow for left turns at the at-grade intersections, another safety feature. To accommodate local people and the adjacent mall, the department has constructed about1.25 miles of new county road to provide access.
"The new roads pick up from existing county roads and go south," Habegger explains. "They will intersect with U.S. 75."
"Keeping traffic flowing has been a challenge with two major highways," Habegger says.
Trafcon, another Nebco company, provided traffic control for the project. That entailed setting up lane closures, signage, cones, drums and arrow boards. As the project has progressed, Trafcon switched traffic as the contractor moved the job forward, explains Randy Morse, President of Trafcon in Lincoln.
Another challenge, Habegger says, was the subsurface water. The project is about 1.5-miles from the Missouri River. The grading subcontractor has dug holes to assess the amount of water and muck at various locations, so department of transportation engineers could decide how far to dig down at each site.
"Any time we dig down 4 to 6 feet, we hit ground water," Habegger says. "We used quite a bit of Geogrid."
Geogrid is a geosynthetic soil-reinforcement product, which comes in rolls. It prevents shifting of the base material. The department used the biaxial product, in a square formation. It has a gritty, sandpaper feel, Habegger explains. Then crushed rock is placed atop the Geogrid.
"It's amazing stuff," Habegger says. "We've used a fair amount. We had areas with complete muck and no bottom. We came in with a foot of rock, put the Geogrid down and then another foot of rock. It pulls on itself and makes itself stable and won't allow itself to sink."
NDOR has been using Geogrid for about 12 years on projects that need soil support. This intersection is at the bottom of a hill and catches all of the water, flowing down from higher elevations and pooling at the intersection. Crews also laid 6-inch, perforated drain tile in a crisscross pattern in the Geogrid to direct the water away from the on and off ramps. The drain tiles flow to a new 48-inch concrete storm sewer to keep the roadway stable.
"Sometimes, it's a headache," Habegger says. "The issue we have run into is the dirt is pretty decent until you get to that area that gets soft."
Trafcon also will install the permanent lane markings using a polyurea system in which it creates a groove about one-quarter-inch deep in the road and places a hot reflective, glass bead material in the groove, which adheres to the pavement. 3M invented the liquid pavement markings in 1999. The system protects the markings from snowplows' scrapings.
"Polyurea is a long-term pavement marking," Morse says. "It lasts several years."
The project is about 70 percent compete, with work scheduled to wrap up and traffic flowing by the end of 2017.